Output control for steam heated heat exchanger

ABSTRACT

A MULTIPLE TOWER GAS DEHYDRATION SYSTEM IS DISCLOSED WHEREIN THE REGENERATION GAS IS HEATED IN A STEAM HEATED HEAT EXCHANGER, WITH THE HEAT EXCHANGER IN OPEN COMMUNICATION WITH A STREAM GENERATOR. AFTER PASSAGE THROUGH THE REGENERATING TOWER, THE REGENERATION GAS PASSES THROUGH DEHYDRATING COMPONENTS, THEN THROUGH A CONTINUOUSLY OPERATED MOTORDRIVEN COMPRESSOR, AND IS RETURNED TO THE WET GAS INPUT. A BYPASS INCLUDING A VARIABLE CONTROL VALVE IS CONNECTED BETWEEN THE RETURN LINE TO THE WET GAS LINE AND THE REGENERATING GAS OUTLET FROM THE TOWERS TO PROVIDE A RECIRCULATING LOOP THROUGH THE REGENERATION GAS DEHYDRATING COMPONENTS AND THE COMPRESSOR. THE VARIABLE CONTROL VALVE IS AUTOMATICALLY SELECTIVELY CONTROLLED IN RSPONSE TO EITHER THE PRESSURE IN THE RECIRCULATING LOOP OR THE DIFFERENTIAL BETWEEN A TIMED FLOW REGULATORY SIGNAL AND THE RATE OF FLOW OF THE REGENERATING GAS THROUGH THE HEAT EXCHANGER, WHEREBY THIS CONTROL VALVE PROVIDES REGULATED CONTROL OVER THE FLOW OF REGENERTION GAS FOR REGULATED GRADUAL CHANGE IN DEMAND UPON THE STEAM GENERATOR.

United States Patent [72] inventor SilvesterQlnonard Bartlesville, Okla.[2!] Appl. No. 789,162 [22] Filed Jan. 6, 1969 [4S] Patented June 28,1971 [73] Assignee Phillips Petroleum Company [54] OUTPUT CONTROL FORSTEAM HEATED HEAT EXCHANGE]! 4 Claims, 1 Drawing Fig.

521 0.8. CI 165/39, 165/108 (5 1] Int. Cl a 86% 1/00 [50} Field oISearch145/108, 39, 40, 62

[56] References Cited UNITED STATES PATENTS 3,203,475 8/1965 Crews etal. 165/108 Primary ExaminerCharles Sukald Attorney-Pendleton, Neuman,Seibold, Williams &

Anderson ABSTRACT: A multiple tower gas dehydration system is disclosedwherein the regeneration gas is heated in a steam heated heat exchanger,with the heat exchanger in open communication with a steam generator.After passage through the regenerating tower, the regeneration gaspasses through dehydrating components, then through a continuouslyoperated motor-driven compressor, and is returned to the wet gas input.A bypass including a variable control valve is connected between thereturn line to the wet gas line and the regenerating gas outlet from thetowers to provide a recirculating loop through the regeneration gasdehydrating components and the compressor. The variable control valve isautomatically selectively controlled in response to either the pressurein the recirculating loop or the differential between a timed flowregulator signal and the rate of flow of the regenerating gas throughthe heat exchanger, whereby this control valve provides regulatedcontrol over the flow of regeneration gas for regulated gradual changein demand upon the steam generator.

. OUT E7 PATENIEU JUN28 IS?! A BmQkDO This invention relates toapparatus for controlling the output of a steam generator. Moreparticularly this invention pertains to apparatus for avoiding suddensubstantial changesin demand upon the steam generator in a gasdehydrating system which utilizes steam for heating the regeneration gasflow.

Various systems are known for dehydrating gas wherein a plurality ofdesiccant beds in dehydrating towers are utilized sequentially witharrangements for circulating a heated gas through the beds forregeneration purposes. The operating cycle of such systems normallyresults in intermittent demand upon the regeneration gas system. Wheresteam is utilized as the heating medium for the regeneration gas, theresult may be sudden high demands upon the steam generator system. Thismay cause water to be carried out from the generator with the steam,particularly in a system wherein the steam flows freely from the steamgenerator to the heat exchanger in response to demand, without controlmeans in the steam supply line. It is desirable thatthe demand for steamfrom the steam generator be controlled to avoid such sudden high steamdemands. It is also desirable that the demand for steam from the steamgenerator be gradually decreased to prevent surging in the boiler firingrate.

It is an object of this invention to overcome the problems indicatedabove.

It is another object of this invention to provide an improved controlarrangement for a steam heated heat exchanger system.

It is a further object of this invention to provide improved controlover the flow of regenerating gas in a natural gas dehydrator system.

Another object of this invention is to provide a gas dehydrator systemhaving a steam heated heat exchanger in the regeneration line withimproved control over the changes in demand upon the steam generator.

Further and additional objects and advantages will appear from thedescription, accompanying drawings and appended claims.

In carrying out this invention in one illustrative form, a natural gasdehydration system is provided including a plurality of dehydratortowers each containing a'desiccant bed, with a control system forcycling heated regeneration gas through one tower while the main flowstream being dehydrated is passed through another of such towers. Theregeneration gas passes through a steam heated heat exchanger, throughthe regenerating tower, which contains dehydrating components such asadsorbents, and through a motor-driven compressor. A recirculating lineis provided for recirculating the regeneration gas through thecompressor, and a variable valve is interposed in the recirculating.line, with control means for gradually adjusting said variable valve toavoid sudden increases or decreases in flow of the regeneration gasthrough the heat exchanger.

For a more complete understanding of this invention, reference shouldnow be had to the embodiment illustrated in the accompanying drawingsand described below, by way of example of the invention.

In the drawing, the single FIGURE comprises a diagrammaticrepresentation of a two-tower gas dehydrator system embodying teachingsofthis invention.

In the drawing, conduit is the input conduit for supplying natural gasto the illustrated system for dehydration. It will be appreciated thatthe input gas may be subjected to pretreatment as desired, e.g., bybeing passed through a gas scrubber (not shown) to extract mechanicallyentrained water, hydrocarbons or thelike.

The conduit 10 leads to a manifold 12 which includes valves 14 and I6and inlet conduits l8 and for selectively directing the gas to adsorbingtowers 22 and 24. A manifold 26 including conduits 28 and 30, and valves32 and 34, connects the towers 22 and 24 with the outlet conduit 36which may be connected to further processing components as desired.

The towers or vessels 22 or 24 are'provided with desiccant beds foradsorbent removal of water, hydrocarbons or the like from the gas beingprocessed. lt will'be appreciated that while one of these towers isconnected between conduits l0 and 36 in the main flow line fordehydrating the gas being processed, the other tower is subjected toappropriate treatment for regenerating and preparing the desiccant forfurther online" dehydrating use.

In the illustration it is assumed that tower 22 is in use fordehydrating the main stream of gas and tower 24 is being regenerated, asindicated by the labels on the towers, the open lines, the arrows, andthe depictions of the various valves.

The regeneration system utilizes gas split-off from the main outletconduit 36 through conduit 38 and one-way valve 39. Conduit 38 leads toa heater 40, comprising a steam heated heat exchanger. A steam generatorfor supplying steam to heat exchanger 40 is illustrated schematically at42 and may comprise a conventional boiler steam generating unit which isconnected to the heat exchanger by an open conduit 44. The rate of heatremoval from the steam, and the attendant rate of condensation in theheat exchanger, determines the steam flow rate from the generator 42 tothe heater 40. The condensate from the steam used in the heat exchangerpasses through conduit 46 into a condensate accumulator 48. Appropriateliquid level controls 50 operate a control valve 51 for exhausting thecondensate.

A conduit 52 leads from the heater 40 to the manifold 26. Manifold 26includes valves 56 and 58 which are connected to the line 52 and toconduits 60 and 62 which are connected to the conduits 28 and 30, forselectively directing the regenerating gas to the towers 22 and 24. Theheated regenerating gas passes upward through the tower on regeneration(tower 24 in the drawing) to the manifold 12. in passing through theadsorbent in the tower the heated gas displaces the adsorbed componentsfrom the desiccant bed therein to reactivate this bed for subsequentonline dehydrating usage.

In the manifold 12, conduits 64 and 66 connect conduits l8 and 20 tovalves 68 and 70 which are in communication with conduit 72 of aregeneration gas treatment line indicated generally at 74. Thisregeneration gas treatment line includes a cooler or condenser 76,conduit 78, a separator or scrubber 80, conduit 82, a motor drivencompressor 84, and conduit 86 which is connected to the input conduit10. The condenser 76 and scrubber 80 function in a conventional mannerto condense and remove by separation the stripped materials, e.g., waterand hydrocarbons, carried from the generating tower by the regenerationgas. Condenser 76 may be a heat exchanger supplied with a cold watercoolant from a supply 88 with exhaust to 90, as illustrated, or othersuitable cooling means. The motor-driven compressor 84 is a continuouslyoperated, constant rate compressor, and provides adequate pressuredifferential to impel the regeneration gas through the regenerationsystem in the manner described.

Control of the rate of flow of the regenerating gas is obtained byproviding a bypass line 92 connecting conduit 86 to conduit 72, with avariable control valve 94 in this line for controlled recirculation ofregeneration gas through a loop circuit comprising conduits andcomponents 72, 76, 78, 80, 82, 84, 86, 92 and 94.

Valve 94 is an appropriate valve for remote positional control, and ispositioned in response to controls 96. The position of this valve isdetermined from two inputs derived from two system conditions and oneexternal control. One of these inputs is the differential between aregulated variable set point, supplied by a timing regulator 100, and asignal representing the flow rate of the regeneration gas throughconduit 38. The other input represents the pressure in the conduit 82.

The apparatus for providing the first noted input to controls 96comprises a flow rate transducer 102, the regulator 100 and a flowcontroller I04. The regulator 100 provides a timecontrolled variableset-point signal to the controller 104. Transducer 102 senses thepressure differential across an orifree 106 in line 38 and provides asignal to the controller 104 corresponding to the flow rate in theconduit 38. The con troller 104 compares the signals received fromregulator 100 and transducer 102 and provides an output control signalrelated to the differential between these input signals. In theillustrated system, utilizing pneumatic controls, regulator 100 mayincludean appropriate cam driven by a timing motor for slowing opening avalve (not shown) to provide a slowly increasing pressure signal tocontroller 104 upon initiation of a regenerating cycle, and a decreasingsignal to controller 104 after the adsorbent hasbeen stripped.Transducer 102 provides a pressure signal representative of the flowrate in conduit 38. Controller 104 serves as a subtractor relay in thatit transmits a pressure signal through conduit 112, to controls 96,which is related to the differential between the pressure inputs fromthe regulator 100 and the transducer 102. lf the pressure input fromregulator 100 exceeds the transducer 102 output, the signal transmittedby controller 104 will increase in accordance with the differentialtherebetween.

A flow recorder 108 may be connected with transducer 102 as desired.

The second input to controls 96 is provided by a pressure controller114. Controller 114 receives a signal from pressure transducer 116 whichis representative of the pressure in conduit 82. In the illustratedsystem, the pressure signal transmitted from controller 114 to controls96, through line 118, is related to the pressure in conduit 82.

Controls 96 effectively select between the two input signals theretofrom controllers 104 and 114, and control the position of valve 94 inaccordance with the selected signal. In the illustrated system, a lowselect relay 120 selects the lower of the two input pressure signalsfrom controls 104 and 114 and positions valve 94 in proportion to thelower signal received, by appropriate positioning of a diaphragm-typemotor 122. As the effective signal received by relay 120 increases, thepres sure signal to motor 122, through line 124 is increased to adjustthe valve 94 toward its closed position. Conversely,'as the effectivesignal to relay 120 decreases, the valve 94 is adjusted towards its openposition.

A control valve 126 is provided to hand regulate pneumatic pressure foroperating the motor 122 to position valve 94 when desired.

The controller 114 transmits a signal which is higher than the signalfrom controller 104 under normal conditions of operation. However, thesignal transmitted by controller 114 will be lower than the signal fromcontroller 104 when controller 104 is set for flow through line 38 andthe flow through line 38 is decreased abnormally below the set point ofcontroller 104, e.g., as a result of malfunction of some part of theregeneration system. Thus, under such conditions, relay 120 of controls96 selects the lower signal from controller 114 and thereby regulatesthe recirculation of gas through the closed loop comprising bypass 92and the line 74.

In operation, the illustrated system normally will provide a pressurechange, Le, a pressure drop, throughout the system in the direction offlow, except across compressor 84. That is, there will be apressure'drop across each component from the inlet conduit to the outletof conduit 36, and from the valve 39 to the inlet to compressor 84. Thecompressor provides an adequate pressure increase to provide return flowtherefrom into inlet conduit 10. Thereby, it will be appreciated thatthe pressure in conduit 86 normally is substantially above the pressurein conduit 72, and there is a corresponding pressure drop across valve94.

When the desiccant in the online dehydrator becomes spent, appropriatecontrols reposition the various valves in accordance with the operatingcycle to switch the flow streams between the dehydrator towers, and thenstart the regulator 100. As a new regeneration cycle is initiated, theregulator 100 provides a slowlychanging signal to controller 104 whichin turn transmits a slowly changing signal to the controls 96 inaccordance with the differential between the inputs from regulator 100and transducer 102. Thus, at the beginning of regeneration of theadsorbent in a tower, the regulator 100 will begin to increase thesetting of controller 104 which will cause the pressure transmitted torelay 120 to be increased. This in turn will cause valve 94 to begin toclose to initiate the flow through line 38, and thereby will cause thepressure from transmitter 102 to controller 104 to follow the setting ofcontroller 104. Thereafter, the controls 96 gradually adjust valve 94toward a closed position in response to the slowly increasing signalgenerated by controller 104 as the set-point from regulator is slowlyincreased.

Since the compressor operates at a substantially uniform rate, theclosing adjustment of valve 94 causes a drop in the pressure in conduit82, and hence in conduit 72, which causes the regenerating gas to flowthrough the conduit 38, the heater 40 and the tower being regenerated.The drop in pressure in conduit 82 decreases the input signal fromcontroller 114 to relay 120, but not lower than the pressure signal fromcontroller I04. Thereby, controller 104 continues to provide a lowersignal than controller 114, and controller 104 remains in control ofvalve 94.

Accordingly, continued gradual increase of the set-point to controller104 by regulator 100 further increases the differential over the actualflow signal from transducer 102 and causes further adjustment of valve94 toward a closed position. This further decreases the recirculatingflow through bypass 92, and causes attendant continued gradual increasein the rate of regenerating flow through heater 40. As the rate of flowof regenerating gas through heater 40 thus is slowly increased, the rateof condensation of steam in heat exchanger 40 will be similarlyincreased for'concomitant gradual increase of demand upon the steamgenerator 42, thereby gradually increasing the steam flow rate until thegenerator boiler is generating at the maximum required rate.

Since the movement of valve 94 in response to controller 104 isdependent upon the differential between the signals from regulator 100and transducer 102, the flow rate through conduit 38 will continue tolag the increasing set-point of regulator 100. Accordingly, the maximumset-point of regulator 100 is such that an equilibrium condition isestablished wherein the differential between the two signals tocontroller 104 is adequate to provide an input to controls 96appropriate to maintain valve 94 in the partially closed positionappropriate to sustain the maximum desired regenerating flow.

When the adsorbent in a tower has been regenerated, the regulator 100will slowly reduce the set-point of controller 104 to zero. Upon suchdecrease of the set-point from regulator 100, the differential betweenthis set-point and the flow signal from transducer 102 willslowlydecrease to slowly open valve 94, and the regeneration flow ratewill decrease accordingly. With the set-point of controller 104 at zero,controller 104 will transmit a signal of zero pressure to relay 120.Relay will transmit a signal of zero pressure to motor 122 which causesvalve 94 to be fully open.

Thus, the described apparatus and method conveniently and economicallyprovide accurate control over the flow of the regenerating gas, withattendant control of the flow through the heat exchanger and thus of thechanges in demand upon the steam generator equipment. The varying loadupon the heat exchanger is accommodated and the attendant changes in therate of flow of steam from the steam generator to the heat exchanger areobtained under the desired control without the use of valves in thesteam line.

A line 130, and control valves 132 and 134, may be provided forbypassing heater 40 to direct dry gas through a tower to cool thedesiccant bed therein subsequent to regeneration and prior to return toonline" use. The described regeneration control system may be programmedto control such cooling flow as desired.

The various valves for controlling the cycling of the illustrated systemmay be positioned by any suitable means, one example being the use ofpiston motor valves, as indicated in the drawing, with the piston motorsbeing operated by a pneumatic control system. Further processingequipment may be included in line 36, or downstream therefrom, asdesired.

It will be appreciated that an improved system and method have beenprovided which meet the aforestated objects.

While a particular embodiment of this invention has been shown, it willbe understood, of course, that the invention is not limited theretosince modifications may be made by those skilled in the art,particularly in light of the foregoing teachings. Therefore, it iscontemplated by the appended claims to cover any such modifications asincorporate those features which may be said to constitute the essentialfeatures of these improvements, within the true spirit and scope of theinvention.

lclaim:

1. Steam heating apparatus including a heat exchanger, steam generatormeans'connected to said heat exchanger for supplying steam thereto, aprimary flow line connected to said heat exchanger, means forcirculating fluid at a predetermined rate, said circulating means beingconnected in said primary flow line for impelling fluid through saidprimary flow line, a recirculating line having one end connected to saidprimary flow line between said heat exchanger and said circulating meansand having its opposite end connected to said primary flow line on theside of said circulating means opposite said first end to provide arecirculating circuit including said circulating means and saidrecirculating line, variable flow control means in said recirculatingline, and means for adjusting said flow control means to control therate of flow of such fluid through said heat exchanger independently ofsaid predetermined rate and thereby to control the demand upon saidsteam generator.

2. Steam heating apparatus as in claim 1 wherein said fluid circulatingmeans is a compressor operated at a uniform rate.

3. Steam heating apparatus as in claim 1 wherein said adjusting meansincludes a timing regulator and provides a control output for saidvariable flow control means which is responsive to said timing regulatorand to the rate of flow through said heat exchanger.

4. Steam heating apparatus as in claim 3 wherein said timing regulatorprovides a predetermined timed input signal, other means provides aninput signal representative of the actual rate of flow through said heatexchanger, and said adjusting means adjusts said flow control means inproportion to the differential between such input signals.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,57,726 Dated June 2'8 197].

Inventor(s) Silvester C. Leonard It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Title page, Primary Examiner "Sukald" should read Sukalo Column 2, line1, "or" (second occurrence) should read and and Column 6, line 1 4(Claim 3), after "flow" insert of such fluid Signed and sealed this 18th day of January 1 972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Patents

